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Solar Energy
Published in Sergio C. Capareda, Introduction to Renewable Energy Conversions, 2019
Solar thermal electric power systems take advantage of the sun's energy and convert it first into thermal energy. However, flat plate collectors do not provide a high temperature, and as a result, the solar energy is usually concentrated and directed to a single absorber. As shown in Figure 2.14, solar energy is directed by numerous heliostats (or reflectors) to reflect the solar energy into a central receiver system (usually a boiler). This boiler will then absorb enormous amounts of solar energy, thereby producing a very high-temperature steam, normally around 950°F [510°C] at around 1,400 psi (95 atmospheres). This superheated steam is then directed to a steam turbine to move the turbine blades, and the turbine shafting is connected to a generator to produce electrical power. This is then connected to the grid. The spent steam goes through a cooling process where it is pumped to a feed water heater before being brought back to the central receiver system. The capacity of these systems may range from a low of 10 MW to as high as 200 MW of electrical power, depending upon the available area for solar energy collection (Bhattacharya, 1983).
Renewable Resource Distributed Generators
Published in H. Lee Willis, Walter G. Scott, Distributed Power Generation, 2018
H. Lee Willis, Walter G. Scott
In order to keep solar reflection on its target point, a heliostat has to vary its angle with the sun half as much as the movement of the sun – a heliostat will move by 90 degrees as the sun moves 180 degrees across the sky during the day. Even when accurately tracked against the sun, an individual heliostat can never provide a constant level of solar energy throughout the day, because its effective area (cross-sectional area of sunlight that strikes it) changes with its angle to the sun. At some point in the day, the mirror will be close to “edge on,” presenting only a small portion of its total surface to the sun. For example, at the minimum time of the day for power production, a 100 meter2 mirror might be at an angle of 15 degrees to the sun, at which time it presents only 26 meters (26%) of perpendicular cross-section to the sun. At other points, it might be close to 90 degrees, presenting a target to the sun that is close to 100% of its surface area. However, it will never reach exactly 100% – to do so it would have to be perpendicular to the sun, in which case it would be aiming the sunlight directly back at the sun.
Concentrating Solar Thermal Power
Published in D. Yogi Goswami, Frank Kreith, Energy Conversion, 2017
Manuel Romero, Jose Gonzalez-Aguilar, Eduardo Zarza
Mature low-cost heliostats consist of a reflecting surface, a support structure, a two-axis tracking mechanism, pedestal, foundation, and control system (Figure 19.46). The development of heliostats shows a clear trend from the early first-generation prototypes, with a heavy, rigid structure, second-surface mirrors, and reflecting surfaces of around 40 m2 (Mavis, 1989), to the current commercial designs with large 100–120 m2 reflecting surfaces, lighter structures, and lower-cost materials (Romero et al., 1991). Since the first-generation units, heliostats have demonstrated beam qualities below 2.5 mrad that are good enough for practical applications in solar towers, so the main focus of development is directed at cost reduction. Two basic approaches are being pursued to reduce per m2 installed cost.
Thermal performance optimization of rectangular cavity receiver for cross linear concentrating solar power system
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Akash Patel, Rajkumar Malviya, Archana Soni, Prashant Baredar
The fundamental component of the heliostat field, represented in Figure 2, consists of four mirror lines and 60 heliostats. On the one mirror line, which is located on the east-west axis, there are 15 heliostats, each measuring 1.5 × 1.5 m. The distance between each mirror line and the heliostats is 3.2 m, and their spacing is uniform at 2.2 m. The receiver line is positioned between the third and fourth heliostats, crossing the mirror lines at an angle. The receiver is set up 15 m above the surface. Because the next mirror blocks the reflected sunlight, heliostats farther from the receiver need to be spaced apart or higher. Therefore, the northern four heliostats are installed on the inclined ground at 13° (Aiba et al. 2016). In the present analysis, the system with one mirror line consisting of 15 heliostats has been considered for investigation.
Recent advances in gas/steam power cycles for concentrating solar power
Published in International Journal of Ambient Energy, 2022
Achintya Sharma, Anoop Kumar Shukla, Onkar Singh, Meeta Sharma
There are mainly four focused areas namely solar field, thermal storage, power block and system efficiency for the advancement of the integrated solar combined cycles to reduce the cost for power generation. The scope of studies for the improvement of the solar field includes the development of high precision durable heliostats for improved optics, wireless control systems for higher reflectivity of heliostats and improved absorber coatings. The prospective study area of thermal storage includes the direct storage concept with higher temperature difference, development of low-cost long-duration energy storage system, superior charging and discharging for enhanced operation strategies. In the power block section, the primary area of interest is the development of standardised design and advanced hybridisation of topping cycle, bottoming cycle and CSP for improved performance. Advancement of the system efficiency is depending on the higher process temperature, adapted turbine design, lower parasitic energy consumption & enhanced control, operation and maintenance procedures.
Thermal performance analysis of a solar-driven supercritical CO2 split-flow recompression Brayton cycle
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2022
Due to the astronomical properties of sunlight and the heavy and complicated control system, heliostats cannot effectively track the sun’s trajectory in real time. Generally, it is feasible for an existing concentration technique to involve the focusing of a single target in sunlight. Through adjusting the heliostats, the light can be reflected to a sole stationary predetermined target. In this technique, the heat flux distribution of the light spot focused on the heating surface of the receiver varies widely in time and space. According to the geometric dimension of the cavity receiver, the heat flux of the heating surface in the receiver at different times is numerically simulated by the aforementioned model shown in Figure 6. The uneven distribution represents a higher heat flux at the center of the spot and decreases away from the spot, which is consistent with the heat flux distribution reported in literature (Hu, Yu, and Wang 2015; Yu et al. 2012). The spot center on the heating surface is on the right side of the heating surface at 9:00 am, and the maximum heat flux is 224 kW·m−2. The central position of the spot moves from right to left continuously with time. The spot on the heating surface is basically symmetrical at 12:00 noon and the maximum heat flux is 349 kW·m−2. At 3:00 pm, the spot is on the left side of heating surface and the maximum heat flux is 215 kW·m−2.